Magnetic resonance imaging (MRI) techniques have been developed for various medical applications. MRI techniques make use of electromagnetic fields to create images of a patient. MRI techniques may allow for the generation of high-quality two- or three-dimensional images of a patient tissue, which can then be examined by a physician for diagnosis purposes. In particular, MRI techniques allow for the generation of internal images of patient's tissue, blood, flesh, organs, or the like, which can be examined to identify problems with the patient and facilitate improved patient care.
MRI devices typically subject a patient to a very strong magnetic field, and then apply pulses or bursts of radio frequency (RF) radiation to an area of the patient to be imaged. The strong magnetic field generally orients the protons of the tissue of the patient in particular directions. However, the RF bursts cause some of the patient's protons to resonate, or spin, at a particular frequency, depending on the local magnetic field. The resonance frequency is often referred to as the Larmour frequency, and has a linear relation with the local magnetic field. When the RF energy burst is terminated, the resonating protons reorient in accordance with the strong magnetic field of the MRI device, giving off energy in the process. The MRI device can detect the energy given off by the reorienting protons to create a high quality image of the patient tissue.
A wide variety of implantable medical devices (IMDs), including active implantable medical devices (AIMDs), have also been developed to monitor patient conditions or possibly deliver therapy to the patient. Some IMDs perform both monitoring and therapeutic functions. One common example of an IMD is a pacemaker. A pacemaker typically includes at least one pacing and sensing lead for sensing cardiac activity and delivery of pacing pulses to the heart. Other examples include implantable brain stimulators, implantable gastric system stimulators, implantable nerve stimulators or muscle stimulators, implantable lower colon stimulators, implantable drug or beneficial agent dispensers or pumps, implantable cardiac signal loops or other types of recorders or monitors, implantable gene therapy delivery devices, implantable incontinence prevention or monitoring devices, implantable insulin pumps or monitoring devices, and so on.
Conventionally, patients that use IMDs are generally discouraged or prohibited from being subjected to MRI. One of the concerns is that, during an MRI procedure, time-varying electromagnetic fields generated by the MRI device may cause energy to be transferred to leads associated with the IMD. It is desirable to overcome this limitation.